SailNet Community - Reply to Topic

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > General Interest > General Discussion (sailing related) > How do you measure the waterline
 Not a Member? 


Thread: How do you measure the waterline Reply to Thread
Title:
  

By choosing to post the reply below you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Message:
Trackback:
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:
 

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Topic Review (Newest First)
07-27-2012 07:11 PM
rbrasi
Re: How do you measure the waterline

I live in Henderson, but have never sailed anywhere but the Pacific Ocean. My boat resides in Marina Del Rey, Ca. I kind of answered my own question there, didn't I?
07-27-2012 02:41 PM
GeorgeB
Re: How do you measure the waterline

Rbrasi, I see that you are from Henderson and I assume you sail in Lake Mead. Is there much river current in the lake? What is your drift rate on a calm day – you could use that as a constant to adjust from speed over ground to boat speed. Don’t get too hung up over theoretical boat speed (THS). After all, it is theoretical and was developed in the age of square riggers which we all can agree have an entirely different hull form. The basic principal is displacement boats have to push water out of the way to move, and after a certain point, they can’t push the water away any faster. As you approach THS, a standing wave will develop at the bow and the stern. In effect leaving your boat in a “hole” between the two. At that point, it requires an enormous amount of energy to pull your boat out of that “hole”. This is when power boats step up onto a plane. About the only way you can do this in a sailboat is to surf a wave or in your case, a wake. Unfortunately you need something along the line of 10-15 kts of boat speed to sustain a surf so for guys like us, the thrill is fleeting. Use your THS speed as a bench mark, kind of like breaking the sound barrier and don’t stress if you aren’t matching it all the time.
07-27-2012 02:01 PM
johnnyquest37
Re: How do you measure the waterline

Quote:
Originally Posted by rbrasi View Post
So, if at 25' LWL, my hull speed calculates to 6.7 Kt. What is the best measure? I currently use a Garmin GPS to get my speed readings, but that is speed over land. How does that translate? I routinely exceed 6.7 with current and a decent wind, according to my Garmin.
The GPS is giving your speed over ground. Hull speed is your theoretical maximum speed through the water. If we are doing 6.9 knots (hull speed for the Hunter 29) through the water, but the water itself if moving with say, 1 knot of current in the direction we are travelling, then the GPS would measure 7.9 knots of speed over ground. Current can help you go faster than hull speed and so can waves. As you slide down the face of the wave, your boat speed will increase. I once clocked 12 knots of SOG while surfing down 5-6' waves and my boat has a theoretical hull speed of 7.4 knots.
07-27-2012 01:46 PM
zedboy
Quote:
Originally Posted by boatingcruising:901784
I get the feeling that reaching optimum hull speed is like getting the advertised gas millage in your car or obtaining the published speed of small aircraft at a set RPMs.
Apples to oranges - hull speed is an approximation of how a displacement hull will move. In flat water it shouldn't be hard to reach (I can even get close in my boat, which has horrific hydrodynamics - motor in well below w/l, ballast bolted to side of keel...

What builders/designers advertise is not hull speed, but polars - which ought to be based on their real world measurements (tho designers may post calculated polars on a design before it's built)

Ability to maintain hull soeed in varying conditions and over a sustained period of time is much trickier than hitting it for a few minutes 135 off the wind on a nice day
07-27-2012 08:25 AM
rbrasi
Re: How do you measure the waterline

So, if at 25' LWL, my hull speed calculates to 6.7 Kt. What is the best measure? I currently use a Garmin GPS to get my speed readings, but that is speed over land. How does that translate? I routinely exceed 6.7 with current and a decent wind, according to my Garmin.
07-26-2012 09:27 PM
boatingcruising
Re: How do you measure the waterline

I am new to sailing but based on conversations with other sailors I get the feeling that reaching optimum hull speed is like getting the advertised gas millage in your car or obtaining the published speed of small aircraft at a set RPMs.

FORMUL: Optimum Hull Speed = Incredible Accomplishment
07-26-2012 07:51 PM
WDS123
Re: How do you measure the waterline

If you ever get to hull speed , please tell us the conditions
07-26-2012 07:03 PM
boatingcruising
Re: How do you measure the waterline

Tks everyone
My goal is to simply have some idea of what the optimum performance of the sailboat would be so I can have a goal to shoot for. I am not into racing, at least not yet!

so if the waterline is 26.92 than the sq root is about 5.18 ( i used the calculator) so the optimum speed should be about 6.95 say 7kn. I hope I can learn to get at least 5.5 - 6 out of the boat.
07-26-2012 06:00 PM
sea_hunter
Quote:
Originally Posted by boatingcruising:901643
How do you measure the waterline on a sailboat? I want to calculate the approximate best speed of my sailboat.
Do I measure the curve of the boat or just a straight line from the bow to the stern on the waterline?
Straight line through center at water line, overall inside toe rail bow to inside toe rail stern through center.
07-26-2012 04:42 PM
chuck53
Re: How do you measure the waterline

Go to sailboatdata.com.
Theres a Hunter 290 listed with a 26.92 waterline.
One foot one way or the other is maybe one tenth of a knot so unless you are into serious racing, it really doesn't matter much.
This thread has more than 10 replies. Click here to review the whole thread.

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


All times are GMT -4. The time now is 06:27 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.